The thermochemical treatment promotes the transformation of their chemical structure under high temperatures. The three main thermochemical treatment processes are combustion, gasification and pyrolysis, which have different operations and consequently generate different products (BELGIORNO, V. et al. Energy from gasification of solid wastes. Waste Management, v. 23, n. 1, p. 1-15, 2003. ISSN 0956-053X.).
The thermochemical processes applied to solid waste have several advantages, such as the reduction of the waste volume generated and the ensuing decrease in the demand for disposal areas; the utilization of the energetic potential of the waste; recovery of chemical compounds and minerals that can be reused for other purposes, and the elimination of some contaminants that may be present in the waste (Stantec Consulting Ltd., WASTE TO ENERGY: A Technical Review of Municipal Solid Waste Thermal Treatment Practices—Final Report. Burnaby, B C, 2011).
Specifically, regarding pyrolysis, object of the present patent of invention, it constitutes a process of heating a fuel (in this case, solid waste) at a given heating rate, in complete absence of oxygen (or in an amount so small that it does not allow gasification to occur), and it may or may not be performed in the presence of a mediating gas, such as nitrogen (BASU, Prabir Biomass Gasification and Pyrolysis: Practical Design and Theory, Burlington: Ed. Elsevier, 2010).
The products of pyrolysis, according to Basu (BASU, Prabir. Biomass Gasification and Pyrolysis: Practical Design and Theory. Burlington: Ed. Elsevier, 2010.), Chen et al. (CHEN, D. et al. Pyrolysis technologies for municipal solid waste: A review. Waste Management, n. 0, 2014, ISSN 0956-053X.) and Chhiti & Kemiha (CHHITI, Y.; KEMIHA, M., Thermal Conversion of Biomass, Pyrolysis and Gasification: A Review. 2013. The International Journal of Engineering And Science, v. 2, n. 3 p. 75-85.), are: a) solid fraction, with generation of coal, which can be used as fuel or in energy production; b) liquid fraction, also called pyrolysis oil, which can be processed into fuels and several chemical products, and c) gas fraction, with the generation of condensable gases, such as H2, CO2, CO, and CH4.
The prior art describes pyrolysis plants for the conversion of waste into fuels.
BRPI0307553 describes a process for producing synthesis gas to be used as gaseous fuel or raw material, and an apparatus for its production, and an apparatus for the production of liquid fuel through a self-sustaining process, through which a slurry of carbonaceous material in water, and hydrogen from an internal source are fed into a hydrogenation reactor under conditions whereby methane-rich gases are generated and fed into a pyrolytic vapor reformer under conditions whereby the synthesis gas, consisting of hydrogen and carbon, are generated. A portion of the hydrogen generated through the pyrolytic vapor reformer is fed through a hydrogen purification filter into the hydrogenation reactor, the hydrogen thereby constituting the hydrogen from an internal source. Molten salt coils are used to transfer heat from the hydrogenation reactor, and the Fischer-Tropsch reactor if liquid fuel is produced, to the vapor generator and the pyrolytic vapor reformer.
US2017283714 describes a system which converts waste into fuel, the waste being inserted into a premix chamber where the material is mixed with paraffin to create a slurry. This slurry is then forwarded to the Pyrolysis Chamber, split into a Superior Pre-Melting Chamber and a Lower Pyrolysis Chamber. In one embodiment, the Lower Pyrolysis Chamber uses Molten Salt as a heat transfer medium to achieve high stable temperatures without causing corrosion of the chamber, or requiring high vapor pressure. The slurry is pumped into the inlet at the top of the Upper Pre-Melting Chamber, where it is rapidly heated and a portion of it turns into vapor. The portion that was not vaporized descends to the Lower Pyrolysis Chamber where it is heated and turned into vapor. The portion that was not turned into vapor is removed and sold. The vapor undergoes further processing.
US2017009141 describes a method for producing bio-oil from lignocellulosic biomass. The method employs Molten Salt Pyrolysis for an efficient and low-cost production of such precursor chemicals directly from the total biomass under moderate conditions (400° C., 1 atm). The lignocellulosic biomass, freely available in renewable wood and plant products, undergoes a moderate-temperature heating process in a eutectic mixture of molten salt with or without a catalyst to generate condensable vapor from the bio-oil precursor or platform chemicals. Condensation of the vapor results in a high performance bio-oil, having a broad distribution of relatively pure chemicals or precursors, such as furfural and acetic acid, depending on the molten salt and the catalysts used and other reaction conditions.
CN105400528 describes an apparatus and a method of rice hull pyrolysis comprising a stainless steel pyrolysis reactor provided with a vacuum feeder in the upper part. The plurality of molten salt heaters is vertically disposed inside the apparatus, and the molten salt heaters of each group are densely distributed inside the reactor.
US2015184079 describes a process for the treatment of plastic waste by direct heating in a pyrolysis liquid, molten salt or metal. The pyrolysis system is built in such a way that segregation of the light and heavy materials takes place inside the pyrolysis chamber. Carbon black is segregated from pyrolysis vapors by a cyclone, and fractions of carbon black can be obtained by installing several cyclones in series in order to produce different qualities of carbon black. The suction or driving force required for removing the vapor/upper slag is supplied by the blower.
CN203764635 describes a pyrogenic solid waste decomposition device that uses molten salt in which the mass to be pyrolysed is immersed.
WO2014008995 describes a method of gasification of carbonaceous raw material, in particular, biomass. According to the invention, molten salt is used to cool and/or heat the components of the system used for gasification, i.e. in particular, the gasification reactors and/or pyrolysis gas lines. The document describes an apparatus for the pyrolysis of expanded styrene in a liquefaction treatment system. The equipment consists of 4 equidistant and vertically positioned tubular pyrolysis vessels surrounded by the heat transfer medium, which could be molten salt, and a heat source, disposed horizontally. Styrene must be broken down before entering the system.
The pyrolysis process is used to reprocess waste, and there are industrial plants of continuous and batch processing. However, this is a minimally feasible process, since it requires several stages of preparation of the raw material, including sorting, grinding, washing and drying operations, as well as the addition of a catalyst, requiring intensive labor, high energy expenditure and a set of equipment for carrying out the steps that precede the processing of the raw material, and for loading the material in the reaction unit.
For example, in the cleaning step, normally used to remove most of the organic matter, stones or dirt, metals and other materials harmful to the pyrolysis process, a considerable amount of water is used, as well as equipment for the removal of metals.
Regarding the feeding systems currently used in industrial pyrolysis plants, the ground raw material is conveyed by a screw-worm, which limits the size of the raw material and demands a large amount of energy for its operation. The mechanical components of the screw-worm are susceptible to damage caused by friction between the raw material and the thread wedges and, additionally, a pressure increase in the vessel being fed leads to a decrease in the flow of raw material and to higher work requirements from the motor, so that pressure peaks can cause damage to the motor and the entire feeding system.
Moreover, despite the pretreatment, many impurities are drawn into the system modules, and the process needs to be interrupted for the removal of undesirable solids, which usually happens at the end of the process. However, impurities along the line impact the efficiency of the process, reducing the heat transfer rate to the system, the reaction volume in the tanks and, consequently, the yield and quality of the final product.
Other drawbacks of the thermochemical systems of prior art are related to the homogenization of the raw material, which utilizes propellers, blades, or rotating tanks which, however, should be avoided due to the corrosive atmosphere and elevated temperatures.
Regarding the means of heating, pyrolysis systems usually have electrical resistances, inductors or direct flame burners. The first two imply a high production cost, requiring its own power plant due to the high demand of electric energy, and the direct flame burners offer poor temperature control, and have a risk of explosion if the flame comes in contact with the product. Another problem in the use of both electric and direct burning systems is energy reuse, since in these configurations there is no efficient way to reuse the energy, making the process even more expensive and thus minimally feasible.
Finally, the continuous pyrolysis systems described in the prior art generally employ a single reactor for the pyrolytic reactions, normally fed by screw-worms directly into the reaction tank, so that the stops for loading and performing maintenance on the feeder interrupt production. Furthermore, most of the pyrolytic processes of the prior art do not use a pressurized environment to develop the reaction, which directly influences the quality of the final product and the process yield, besides the fact that they need a previous stage of pretreatment of the residue.
Thus, in order to provide an economically feasible and environmentally safe system, the object of the present patent of invention is a thermochemical treatment system for plastic and/or elastomeric waste in which the thermochemical treatment steps are carried out in a set of three reactors connected in series, increasing the safety and control of the process, with the pyrolysis step being carried out under conditions of positive pressure and temperature above 300° C., upon indirect heating by coils which conduct molten salt through the mass to be pyrolysed, and which includes the separation of gases and liquids, continuous removal of the solid fraction, and elimination of the previous treatment step of the plastic and/or elastomeric material.